Fluorescent lamp including a multi-ringed bulb

ABSTRACT

There is provided a multi-ringed bulb including a plurality of ring bulbs in which a plurality of straight tube portions having an outside diameter of from 12 to 20 mm are connected to each other through bent portions on a same plane. Electrodes are provided hermetically at respective ends of outermost and innermost bulbs of the plurality of ring bulbs. A connection portion connects other adjacent ends of the outermost and innermost bulbs to each other so that the outermost and innermost bulbs communicate with each other, to form a single discharge path. A phosphor layer is formed on inner surfaces of at least the straight tube portions  5   a  of the inner and outer bulbs. The multi-ringed structure bulb is filled with discharge medium. The above-mentioned structure permits to provide a fluorescent lamp and a lighting apparatus, which have a small strain in the inner and outer bulbs, a high strength and an excellent luminous efficiency.

TECHNICAL FIELD

The present invention relates to a fluorescent lamp and a lightingapparatus utilizing such a fluorescent lamp.

BACKGROUND OF THE INVENTION

As a conventional double-ringed fluorescent lamp, there is known, forexample, as shown in FIG. 21, a double-circular fluorescent lamp 321. Insuch a double-circular fluorescent lamp 321, there is provided, on theouter side of an inner ring glass bulb 322 having ring shape, an outerring glass bulb having a ring shape and a larger diameter than the innerring glass bulb so as to be placed concentrically on the same plane. Aconnection portion 324 connects respective discharge paths of the innerand outer ring glass bulbs 322, 323 to each other to form a singledischarge path so that an increased length of the discharge path canenhance the total luminous flux and the luminous efficiency (asdisclosed, for example, following Patent Document 1).

Such a kind of fluorescent lamp has an increased length of the dischargepath in comparison with the other lamp, which is composed of a singlering bulb, thus enhancing the total luminous flux and the luminousefficiency.

Patent Document 1: Japanese Patent Laid-open (KOKAI) Publication No. HEI9-129180.

However, in a manufacturing process of the conventional double-circularfluorescent lamp 321 disclosed in the above Patent Document 1, aprotection layer and a phosphor layer are formed on inner surfaces oftwo straight tubular glass bulbs 322, 323, and then these bulbs areheated to be softened and wound around cylindrical drums so as to bebent into a ring shape. Accordingly, there is a problem that fissure,flaking off or crack may easily occur on the protection layer or thephosphor layer.

After completion of the ring-shape bending process for the ring glassbulbs 322, 323, the connection portion 324 is formed. However, it is notalways easy to carry out the formation process of the connection portion324, and the strength of the connection portion 324 is apt to bedeteriorated, thus causing problems. More specifically, the inner andouter ring glass bulbs 322, 323 are heated so as to be softened in theirentirety and subjected to the bending process. Then, flame from a burneris blown onto portions of these bulbs, on which the connection portion324 is to be formed, to heat them locally to soften, and at this time,gas is blasted into the glass bulbs 322, 323 so that bulb walls thereofproject outward under the function of the gas pressure and are broken byblast to form apertures thereon. Then, the blast-broken ends of theseportions as projected outward are connected to each other by fusion(i.e., the burner blast breaking) so that these apertures communicatewith each other to form the connection portion 324.

The heating process through the burner blast breaking is carried out toblow the flame from the burner onto the portions of the inner and outerring glass bulbs 322, 323, on which the connection portion is to beformed, to heat them to soften, in a state that residual strain causedby the heating in the bending process still exists on the glass bulbs322, 323 in their entirety. As a result, damage such as crack may easilyoccur on the connection portion 324 or in the vicinity thereof. Theglass bulbs 322, 323 are provided on their respective ends with grooveportions “m” formed thereon, which are utilized to carry out the bendingprocess. The connection portion 324 cannot be formed in the vicinity ofthe groove portion “m” and must be formed apart from the end of thebulb. This leads to a decreased length of the discharge paths of thebulbs 322, 323, thus deteriorating the luminous efficiency.

In addition, the burner blast breaking process must be carried out tocouple partially a convexly arched outer surface of the inner ring glassbulb 322 and a concavely arched inner surface of the outer ring glassbulb 323 to each other in a narrow gap (for example, of from 1 mm to 3mm) between the inner and outer ring glass bulbs 322, 323, so as to formthe connecting portion 324, as shown in FIG. 22. Therefore, it is noteasy to carry out the coupling operation due to difference in radius ofcurvature between the opposing circumferential surfaces of the bulbs,thus causing problems.

Each of the inner and outer ring glass bulbs 322, 323 is formed into aring shape as shown in FIGS. 21 and 22, and there is formed a spacehaving a trapezoidal shape between the outer end surfaces 327 a, 328 a,in the axial direction of the tube, of electrode-sealed end portions327, 328 by which a pair of electrodes 325, 326 are sealed,respectively, and the opposing outer end surfaces 329 a, 330 a on theside of the connecting portion 324 in the circumferential direction sothat the distance “La” between the end surfaces 327 a and 329 a issmaller than the distance “Lb” between the end surfaces 328 a and 330 a.

The increased distances “La”, “Lb” on the side of the outer peripheralsurfaces in such a trapezoidal space results in the decreased length ofthe discharge path of the whole fluorescent lamp 21. Accordingly, anon-luminous or dark area is increased, a base 331, which is mountedbetween the electrode-sealed end portions 327, 328 and the opposing endson the side of the connecting portion 324 so as to cover them, is formedinto a fan shape and has a large size, thus causing problems.

DISCLOSURE OF THE INVENTION

An object of the present invention, which was made in view of theabove-described circumstances encountered in the prior art, is thereforeto provide a fluorescent lamp and a lighting apparatus, which have asmall strain in bulb, a high strength and an excellent luminousefficiency.

A fluorescent lamp of the present invention comprises:

a multi-ringed structure bulb including: a plurality of ring bulbs inwhich a plurality of straight tube portions having an outside diameterof from 12 to 20 mm are connected to each other through bent portions ona same plane, the ring bulbs being placed concentrically on the sameplane; electrodes provided hermetically at respective ends of outermostand innermost bulbs of the plurality of ring bulbs; and a connectionportion connecting other adjacent ends of the outermost and innermostbulbs to each other so that the outermost and innermost bulbscommunicate with each other to thereby form a single discharge path;

a phosphor layer formed on inner surfaces of at least the straight tubeportions of the multi-ringed structure bulb; and

a discharge medium with which the multi-ringed structure bulb is filled.

Each of the ring bulbs is composed, into a polygon such as a rectangularshape, of the plurality of straight tube portions and the bent portionsthrough which the straight tube portions are connected to each other.The bent portion may be formed by partially bending a single straightbulb, or carrying out a mold-forming when connecting the ends of thestraight bulbs to each other, or connecting bent bulbs having forexample a U-shape or L-shape to each other or in combination with thestraight bulbs.

The straight tube portion has the outside diameter of from 12 to 20 mmand the optimum outside diameter thereof is within the range of from 14to 18 mm, taking into consideration lamp characteristic property such asluminous efficiency and manufacturing conditions. Although it isconceivable that the outside diameter of the straight tube portion,which is disposed in the vicinity of the bent portion, may vary slightlyduring the forming process of the bent portion and be partially out ofthe above-mentioned range, only a requirement that the outside diameterof the straight tube portion for the most part is within theabove-mentioned range, suffices in the present invention.

It is known that the decreased diameter of the fluorescent lampgenerally enhances the luminous efficiency. In the present invention,the outside diameter of the straight tube portion is limited to 20 mm orless. The outside diameter of the straight tube portion of 20 mm or lesscan provide luminous efficiency, which is comparable to or higher thanthe conventional smaller-diameter circular structure fluorescent lamp.

With the outside diameter of the straight tube portion of less than 12mm, it is difficult to ensure the mechanical strength for the glass bulbhaving the bent portion, resulting in inapplicability. In addition,luminous power, which is comparable to the conventional circularstructure fluorescent lamp having the same size, cannot be obtained,resulting in impracticality.

In order to enhance the luminous efficiency of the conventional circularfluorescent lamp (type name of “FCL”) having the outside diameter of 29mm by at least 10%, it is necessary to reduce the outside diameterthereof to 65% or less. More specifically, the outside diameter of thestraight tube portion of 18 mm or less suffices. Such an outsidediameter can provide satisfactorily a low-profile fluorescent lamp. Itis preferable to limit the outside diameter of the straight tube portionto 14 mm or more, taking into consideration the characteristicproperties such as luminous power and luminous efficiency.

The ring bulbs each of which is formed of a single bulb have at leastthree respective straight tube portions. The number of the bent portionsthrough which the straight tube portions are connected to each other intheir inside, is smaller than the number of the straight tube portionsby one. The bent portions are disposed between the plurality of straighttube portions so that the straight tube portions are disposed onsubstantially the same plane.

The ring bulb is formed into a ring shape so as to surround the centerof the polygon. Concentric connection of the ring bulbs forms the singledischarge path, which surrounds the center of the ring bulbs severaltimes. More specifically, the straight tube portions of each of the ringbulbs are connected to each other in their inside through the bentportions, and a pair of electrodes are arranged at the respective endsof the ring bulbs so as to form a single discharge path. All thestraight tube portions need not always to have the same length and onlyone of them may have the different length. When the four straight tubeportions having the same length are connected through three bentportions, the straight tube portions of the bulb forms a rectangularshape. In this case, the outside ring bulb has the rectangular shape,which is larger than that of the inside ring bulb.

According to the present invention, in the manufacturing process of thering bulb, a single elongated straight bulb having the inner surface onwhich layers such as a phosphor layer has previously formed is heatedlocally only at bent-portion-formation prearrangement portions, i.e.,portions of the ring bulb, on which the connection portions are to beformed, and alternatively, only the corresponding ends of a plurality ofstraight bulbs, which are to be connected to form the connectionportion, are heated locally, and the remaining portions of the bulb arenot subjected to a heating process. It is therefore possible to restrainthe deterioration of the phosphor caused by the heating of the wholering bulb, enhance the initial luminous flux and improve the luminousflux maintenance factor. The local heating of the bulb provides areduced strain of glass and an increased strength thereof.

Even when the connection portion is formed at the corresponding endportions of the ring bulbs by the burner blast breaking process, thestraight tube portions of the ring bulbs have a low strain in glass,thus making it possible to prevent cracks from occurring on the bulbsduring the connection process and improve the strength of the connectionportion.

In addition, the discharge path sections of the plurality of ring bulbsare connected by means of the connection portion to thereby form asingle discharge path, thus making it possible to increase the length ofthe discharge path and enhance both of the total luminous flux and theluminous efficiency.

In a preferable case of the fluorescent lamp, the ring bulb is formed bybending a single straight tube bulb, the straight tube bulb has a tubelength of from 800 to 2500 mm, and a length of a bent-portion-formationprearrangement portion, which is to be formed into the bent portion, iswithin the range of from 15 to 50% of a total length of the straighttube bulb.

Deterioration of the initial luminous flux is restrained effectively,with an increased ratio of the total length of the straight tubeportions, which are not susceptible to the deterioration of the phosphorcaused by heat, relative to the full length of the bulb, thus providingan improved effect in luminous power. In view of this fact, the lengthof the bent-portion-formation prearrangement portion, which is to bethereafter formed into the bent portion, is limited to 50% or less ofthe total length of the straight tube bulb. With the length of thebent-portion-formation prearrangement portion of over 50%, thedeterioration of the phosphor caused by heat during the bending processbecomes serious, thus reducing an improved effect in luminous power. Onthe other hand, with the length of the bent-portion-formationprearrangement portion of less than 5%, particularly less than 15%, itbecomes difficult to carry out the bending process and ensure thedesired mechanical strength of the bent portion.

The length of the bent-portion-formation prearrangement portion, whichis to be formed into the bent portion, is within the range of from 5 to50% of a total length of the straight tube bulb so as to ensure anappropriately increased total length of the straight tube portionshaving the phosphor layer, which is not susceptible to the deteriorationcaused by heat, thus making it possible to provide the fluorescent lamp,which can be manufactured easily, and has an ensured mechanical strengthand a remarkably improved effect in luminous power.

In a preferable case of the fluorescent lamp, each of the straight tubeportions has a length “l” of from 150 to 500 mm and a radius ofcurvature “r” of the bent portion satisfies an expression of“0.03≦r/l≦0.3.

The fluorescent lamp of the present invention utilizes, as a mainluminous power, light radiation from the straight tube portions in whichthe phosphor layer is not susceptible to the deterioration caused byheat, resulting in necessity to ensure the length “l” of the straighttube portion as large as possible. In order to obtain appropriateilluminance for a lighting apparatus for common use, the length “l” ofthe straight tube portion is set within the range of from 150 to 500 mm,and preferable of from 180 to 400 mm.

The radius of curvature “r” of the inner surface of the bent portionrepresents a size of the bent portion, with the result that the lengthof the bent-portion-formation prearrangement portion increases withincreasing radius of curvature “r” and the luminous power reducesaccordingly. To the contrary, the smaller radius of curvature “r” leadsto a larger degree of deformation of the bulb during the formation ofthe bent portion, resulting in difficulty in the manufacture and thepossible deterioration of the strength of the bulb. In view of thesefacts, the present inventors have carried out extensive studies about abalance between the luminous power and formability of the bent portionand obtained findings that the optimum balance can be obtained bylimiting the ratio of the radius of curvature “r” relative to the length“l” of the straight tube portion within a predetermined range.

In case where the length “l” of the straight tube portion is within therange of from 150 to 500 mm, with the ratio “r/l” of the radius ofcurvature “r” of the inner surface of the bent portion relative to thelength “l” of the straight tube portion of less than 0.03, a degree ofdeformation of the bent portion becomes large, resulting in difficultyin the manufacture. In addition, the strength of the bent portion isdecreased due to factors that, when stress of deformation is applied tothe bulb, the bent portion is susceptible to local stress concentration,leading to a possible breakage thereof. Therefore, the above-mentionedcondition is not acceptable. On the other hand, with the ratio “r/l” ofover 0.3, the ratio of the bent portion relative to the ring bulbincreases, with the result that influence due to the deterioration ofthe phosphor caused by heat becomes large, thus leading to a reducedluminous efficiency. Therefore, such a condition is not acceptable.

The radius of curvature “r” of the bent portion satisfies the expressionof “0.03≦r/l≦0.3” in this manner in the case where the length “l” of thestraight tube portion is within the range of from 150 to 500 mm, thusmaking it possible to easily form the bent portion and minimize theinfluence due to the deterioration of the phosphor of the bent portion,which is caused by heat, to effectively utilize the luminous power fromthe straight tube portion.

In a preferable case of the fluorescent lamp, the multi-ringed bulbcomprises a double-tube bulb having inner and outer bulbs,electrode-side outer ends of the inner and outer bulbs at which a pairof electrodes are hermetically provided, respectively, and other outerends thereof, which has the connection portion, are spaced apart fromeach other by a predetermined distance so as to face each other, and abase is disposed on one ends and other ends of the bulbs so as to coverrespective ends thereof.

Here, the phrase “the outer ends . . . so as to face each other” meansnot only a case where the respective outer ends of the bulbs face eachother so that the straight tube portions by which the end sides of therespective bulbs are formed are aligned with each other in their axes,but also another case where the respective outer ends of the bulbs donot face directly each other, but face each other by an angle so thatthe axes of the straight tube portions by which the end sides of therespective bulbs are formed, intersect at an angle of about 90 degrees.

The electrode-side outer ends of the inner and outer bulbs at which thepaired electrodes are hermetically provided, respectively, and otherouter ends thereof, which has the connection portion, are spaced apartfrom each other by a predetermined distance so as to face each other,thus making it possible to decrease the gap between the opposite endsand increase the length of the discharge path as large as possible. Thisalso makes it possible to reduce the dark areas at the opposite ends andmake size and weight reduction of the bases, which are mounted at theopposite ends.

In a preferable case of the fluorescent lamp, the inner and outer bulbsconnected to each other through the connection portion are cut by fusionat the other outer ends thereof and closed hermetically, and the minimumlength from the outer ends to the connection portion is equal to or lessthan 15 mm.

The whole of inner and outer bulbs are not bent, resulting in that thereis no need to form any groove for a chuck as in the conventionalcircular bulb and the end of the bulb can be sealed by a fusion cutting.Here, the fusion cutting of the end of the bulb means the heating of theintermediate portion of the bulb in a molten state to thermally bond thepipe walls of the bulb together at around the central axis of the bulb,thus providing a seal utilizing only the material of the bulb, withoutusing a separate sealing member such as a dummy stem. The sealed end ofthe bulb, which is formed by the fusion cutting, may have a shape with aflat surface in parallel with the perpendicular direction to the axialdirection of the bulb or may have a projecting hemispherical shape. Thefusion cutting of the end of each of the bulb makes it possible todecrease the minimum length between the outer end of each of the otherends of the inner and outer bulbs (i.e., the other ends thereof on theside of the connection portion) and the connection portion to 15 mm orless, thus reducing the dark area. It is therefore possible to increasethe luminescent area of the bulb and the length of the discharge paththereof by the reduced length of the dark area.

In a preferable case of the fluorescent lamp, each of the inner andouter bulbs is formed into a rectangular shape and both electrode-sideends of the inner and outer bulbs extend to corners of the rectangularshape.

This enables the dark area due to shade of the electrode to bepositioned within the base so as to be covered with the base, thusenhancing luminous intensity of the fluorescent lamp. The electrode-sideends of the inner and outer bulbs extend toward the connectionportion-side ends thereof, thus making it possible to increase the totallengths of the inner and outer bulbs by the extended lengths asmentioned above and increasing the length of the discharge path.

When the both electrodes are arranged outside of the corner portions ofthe fluorescent lamp having the rectangular shape, the luminescent areais provided at all the corners of the rectangular shape (i.e., the fourcorners). Accordingly, even when the fluorescent lamp emits light at anyangle around the center of the rectangular shape, the light emissionalways occurs at each of the respective corner portions (i.e., the fourcorners). Thus, uniformity ratio of illuminance of the entirefluorescent lamp can be improved in this manner.

In a preferable case of the fluorescent lamp, the bulbs are filled withmercury vapor serving as the discharge medium, the connection portion isprovided so that a least a part of the connection portion issubstantially flush with the other outer ends of the inner and outerbulbs, and the electrode for the outer bulb extends to a position apartfrom the end thereof by a distance, which is larger than a distance bywhich the electrode for the inner bulb extends to a position apart fromthe end thereof.

This causes the discharge path to be formed also in the vicinity of theend surfaces of the other ends of the inner and outer bulbs, thusleading to occurrence of light emission around the end surfaces. It istherefore possible to increase the luminescent area of the luminescentlamp and the length of the discharge path.

The electrode for the outer bulb extends to a position apart from theend thereof by the distance, which is larger than the distance by whichthe electrode for the inner bulb extends to a position apart from theend thereof, so that the cold spot can be generated in the vicinity ofthe electrode-sealed end portion of the outer bulb to control thepressure of the mercury vapor.

In addition, in a preferable case of the fluorescent lamp, theelectrode-side outer end of at least one of the inner and outer bulbsterminates at a position, which is disposed on an inner side in an axialdirection of the bulb relative to the electrode-side outer end of theother bulb, and electricity receiving devices are arranged on an outersurface of the base covering both the electrode-side outer ends of theinner and outer bulbs in corresponding positions in a space extendingoutward from the electrode-side outer end of the one of the inner andouter bulbs in the axial direction thereof.

This makes it possible to provide base pins such as the electricityreceiving devices on the outer surface of the base in a space extendingoutward from the electrode-side outer end of the one bulb in the axialdirection thereof, thus leading to an effective utilization of the spaceand providing the base having a smaller size.

The fluorescent lamp of the present invention may further comprise asecond electrode disposed at the end of the bulb, which corresponds toan intermediate position of the discharge path.

When the starting voltage from a glow switch device is applied betweenany one of the paired electrodes (hereinafter referred to as the “firstelectrodes”) provided at the ends of the bulbs, which correspond to theopposite positions of the single discharge path formed in the bulbs, andthe second electrode, the discharge occurs in a part of the dischargepath. The length between the one of the first electrodes and the secondelectrode is smaller than the length of the discharge path of the wholeluminescent tube so that the starting voltage between the one of thefirst electrodes and the second electrode is lower in comparison withthe case where starting voltage is applied between the first electrodesof the illumination tube. Subsequent occurrence of the discharge on theother of the first electrodes makes it possible to reduce the generalstarting voltage of the illumination tube.

In the present invention, the distance between the one of the firstelectrodes and the second electrode is smaller than that between thepair of electrodes. When, prior to the occurrence of the dischargebetween the pair of electrodes to illuminate the fluorescent lamp, thedischarge is caused to occur between the one of the first electrodes andthe second electrode of the bulbs, and the discharge is then caused tooccur between the pair of electrodes, the starting voltage for theillumination tube can be reduced. Alternatively, it is possible to causea primary discharge for illumination to occur only between the one ofthe first electrodes and the second electrode, to provide a dimmerillumination of the fluorescent lamp.

In a preferable case of the fluorescent lamp, centers of radii ofcurvature of inner and outer surfaces of bent portions of the inner andouter bulbs substantially coincide with each other and the bent portionshave a diameter, which is substantially identical to the diameter of thestraight tube portions disposed in the vicinity of the bent portions.

The double-tube bulb is constructed by combining the inner ring bulb andthe outer ring bulb together, which have similar figures to each other,but are different in the maximum ring diameter from each other. Theinner and outer ring bulbs are connected to each other at their endsthrough the connection portion in a state that they are placedconcentrically with each other so that the corresponding bent portionsface each other.

The ring bulbs are connected to each other so that the centers of radiiof curvature of the inner and outer surfaces of the bent portions of theinner and outer bulbs substantially coincide with each other, and thecenters of radii of curvature of the inner and outer bulbs alsosubstantially coincide with each other. The phrase “the centers of radiiof curvature of . . . substantially coincide with each other” means thatthe centers of radii of curvature are identical to each other orslightly displaced from each other. In term of the functions of thepresent invention, it is acceptable that the distance between thecenters is equal to or less than 10% of the radius of curvature, andpreferably, equal to or less than 5% thereof.

The radii of curvature of the corresponding bent portions of the innerand outer ring bulbs substantially coincide with each other so that thedistance between the adjacent bulbs is substantially identical with eachother over the bent portions and the straight portions. In this case, itis also acceptable that the distance between the centers is equal to orless than 10% of the radius of curvature, and preferably, equal to orless than 5% thereof.

Substantial coincidence of the centers of radii of curvature of the bentportions of the inner and outer ring bulbs, when these bulbs areconnected concentrically with each other, makes it possible to ensurethe state that the distance between the adjacent bent portions issubstantially equal to the distance between the adjacent straightportions, in comparison with the case where the plurality of fluorescentlamps having the same radius of curvature of the bent portions, arearranged in the same manner. Therefore, an improved external appearancecan be provided and luminance can be made uniform. It is preferred tolimit the distance between the bent portions as well as the distancebetween the straight portions within the range of from 3.0 to 10 mm.

The tube diameter of the bent portion is substantially identical to thetube diameter of the straight portion. The tube diameter of the bentportion is defined on the basis of a tube diameter on a cross-sectionalplane of the bulb tube, which is perpendicular to a direction that isdirected radially from the center of an imaginary ring-shaped planealong and in parallel therewith, and when the tube is out-of-round, butslightly flattened, it is defined on the basis of an average tubediameter. The phase “substantially identical” means that the tubediameter of the bent portion is up to plus or minus 10% of the tubediameter of the straight portion.

Such formation of the bent portions causes a person to visuallyrecognize as if the bent portions of the ring bulb in its externalappearance continue from the straight tube portion to form a curvedline. Therefore, an improved external appearance of the luminescent tubecan be provided and there is no formation of a local area having a lowertemperature, when illuminating. As a result, the cold spot cannot begenerated easily, and the bent portion is not susceptible to occurrenceof blackening or stain due to condensed mercury.

The length of the straight tube bulb is substantially identical to thelength of the discharge path. In view of obtaining luminous power, whichis comparable to the conventional smaller-circular structure fluorescentlamp, the length of the straight tube bulb is within the range of from800 to 2500 mm.

In a preferred case of the fluorescent lamp, each of the ring bulbs isformed into a rectangular shape by four straight tube portions, threebent portions are placed at three diagonal positions of the rectangularshape and the base is placed at a remaining one diagonal positionthereof.

This makes it possible to provide a light source in which the mainluminescent areas are formed on the respective sides of the rectangularshape. The base is placed on the diagonal line of the rectangular shape,thus making it possible to increase the length of the luminescent areaas large as possible. In addition, limitation of the number of bentportions to three can provide an easy formation of the bulb.

In a preferred case of the fluorescent lamp, each of the ring bulbs isformed into a rectangular shape by five straight tube portions, the bentportions are placed at diagonal positions of the rectangular shape andthe base is placed at a central position of one side of the rectangularshape.

This makes it possible to provide a light source in which the mainluminescent areas are formed on the respective sides of the rectangularshape. The base is placed at the central position of the one side of therectangular shape so that the opposite end portions of the bulb isaligned with each other in the same line, thus providing a structure foreasily mounting the base.

In another aspect, the lighting apparatus of the present inventioncomprises: a main body; the plurality of fluorescent lamps as describedabove; and a high frequency lighting circuit, which supplies lampelectricity to the fluorescent lamps at a high frequency of at least 10kHz.

The main body may be a ceiling surface mounted type, a ceiling pendanttype or a wall surface mounted type, or a type provided with a glove, ashade or a reflector, or a type provided with an exposed typefluorescent lamp or a light guiding plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a fluorescent lamp according to a firstembodiment of the present invention;

FIG. 2 is a front view of a fluorescent lamp according to a secondembodiment of the present invention;

FIG. 3 is a front view of a fluorescent lamp according to a thirdembodiment of the present invention;

FIG. 4 is a front view of a fluorescent lamp according to a fourthembodiment of the present invention;

FIG. 5 is a front view of a fluorescent lamp according to a fifthembodiment of the present invention;

FIG. 6 is a front view of a fluorescent lamp according to a sixthembodiment of the present invention;

FIG. 7 is a front view of a fluorescent lamp according to a seventhembodiment of the present invention;

FIG. 8 is a front view of a fluorescent lamp according to a eighthembodiment of the present invention;

FIG. 9 is a front view of a fluorescent lamp according to a ninthembodiment of the present invention;

FIG. 10 is a front view of a fluorescent lamp according to a tenthembodiment of the present invention;

FIG. 11 is a view along the viewing line XIA-XIA and the viewing lineXIB-XIB;

FIG. 12 is a front view of a fluorescent lamp according to a eleventhembodiment of the present invention;

FIG. 13 is a schematic front view of a fluorescent lamp, partially cutaway, according to a twelfth embodiment of the present invention;

FIG. 14 is a schematic front view of a fluorescent lamp provided with abase of the present invention;

FIG. 15 is a schematic block diagram of a high frequency lighting deviceof the present invention;

FIG. 16 is a view illustrating a front side of a fluorescent lampaccording to a fourteenth embodiment of the present invention and aschematic block diagram of a high frequency lighting device of thepresent invention;

FIG. 17 is a schematic front view of a fluorescent lamp, partially cutaway, according to a fifteenth embodiment of the present invention;

FIG. 18 is a front view of fluorescent lamp according to a sixteenthembodiment of the present invention;

FIG. 19 is a front view of the fluorescent lamp, partially in anenlarged scale, as shown in FIG. 18;

FIG. 20 is a front view of a fluorescent lamp according to a seventeenthembodiment of the present invention;

FIG. 21 is a front view of a conventional double-circular fluorescentlamp; and

FIG. 22 is an enlarged view of a region of XXII as shown in FIG. 21.

BEST MODE FOR EMBODYING THE INVENTION

Hereunder, preferred embodiments of fluorescent lamps and lightingapparatus of the present invention will be described in detail withreference to the accompanying drawings. In the drawings, the samereference numerals are given to the same or corresponding components andrepetitive description will be omitted with the exception ofspecifically required description.

FIG. 1 is a front view of the fluorescent lamp 1 according to the firstembodiment of the present invention. The fluorescent lamp 1 isstructured by disposing, outside an inner bulb 2 having a rectangularshape in its front view, an outer bulb 3 having a rectangular shape,which is slightly larger than the inner bulb 2 and substantially similarthereto so as to be placed concentrically with the inner bulb 2 at apredetermined gap “g” and connecting these bulbs to each other through aconnection portion 4 to thereby form a single unit of double tube (adouble-tube bulb).

These inner and outer bulbs 2 and 3 are formed of glass bulbs 5, 5,respectively, each of which is composed of four straight tube portions,each having a circular cross section, substantially into a square shapeso that an intersecting point of diagonal lines of this square shape isplaced at a point “O”. The glass bulbs 5, 5 are formed of soft glasssuch as soda lime glass or lead glass and they may be formed of hardglass such as borosilicate glass or silica glass.

These glass bulbs 5, 5 are filled with discharge medium including a raregas and mercury. The rare gas is argon (Ar) gas and its chargingpressure is about 320 Pa. The rare gas with which the inner and outerbulbs 2, 3 are filled, may include argon, neon or krypton. At least oneof the glass bulbs 5, 5 may include amalgam therein. The amalgam is analloy of mercury and material, which can be alloyed with the mercury.The amalgam of, for example, zinc-mercury may be included for the chargeof mercury at a required amount. The amalgam may have a shape ofpellets, columns or plates.

The amalgam is received in small tubes provided in stems, which areattached to the ends of the glass bulbs 5, 5. The amalgam isstationarily placed or received in any one of these positions through amelting process or a mechanically holding member. Alternatively, theamalgam may be received in the bulb so as to be movable therein. Bydisposing the amalgam such as Bi—Sn—Pb or Bi—In for controlling thepressure of mercury vapor in the glass bulbs 5, 5, the fluorescent lamp1 can be lightened at the optimum state even when the ambienttemperature becomes relatively high.

Each of the glass bulbs 5 is provided on its inner surface with aprotective layer 6, which includes metallic oxide particles, i.e.,alumina (Al₂O₃) fine particles and has a thickness of about 1.0 μm. Theprotective layer 6 is preferably composed of the metallic oxideparticles, for which known particles such as alumina (Al₂O₃) or silica(SiO₂) may be used. The protective layer 6 is provided on its innersurface with a phosphor layer 7 that includes three band fluorescenttype phosphor particles and is formed all over the length of theprotective layer. The phosphor layer 7 is formed in a thickness of about20 μm by applying the three band fluorescent type phosphor particleshaving a correlated color temperature of 5000K in an amount of from 4.0to 7.5 mg/cm², preferably of from 6.0 to 7.5 mg/cm², and subjecting themto a drying and sintering process.

The fluorescent lamp 1 is not a lamp, which is bent in its entirety asin the conventional circular structure fluorescent lamp, but is merelysubjected to a local bending process. It is therefore possible toincrease an applied amount of phosphor and minimally restrain the layerfrom being peeled off, thus providing an increased thickness of thephosphor layer 7. Accordingly, the initial luminous flux can beenhanced.

It is preferable to previously form the phosphor layer 7 on at least thestraight portion 5 a, prior to the formation of the bent portion 5 b.However, the present invention is not limited only to such a preferablecase, and the phosphor layer 7 may be formed after the formation of thebent portion 5 b. Known phosphor such as three-band fluorescent typephosphor or halophosphate are applicable as the phosphor for forming thephosphor layer 7. It is however preferable to use the three-bandfluorescent type phosphor in view of luminous efficiency.

Concerning the three-band fluorescent type phosphor, BaMg₂Al₁₆O₂₇:Eu²⁺isapplicable as the blue type phosphor having a luminescent peakwavelength in the vicinity of 450 nm, (La, Ce, Tb)PO₄ as the green typephosphor having the luminescent peak wavelength in the vicinity of 540nm, and Y₂O₃:Eu³⁺as the red type phosphor having the luminescent peakwavelength in the vicinity of 610 nm. However, the present invention isnot limited only to use of these materials or substances.

Each of the glass bulbs 5 has four straight tube portions 5 a and threebent portions 5 b, which are placed in an interconnecting state on thesame plane so that the four straight tube portions 5 a form therespective sides of a square shape. In this case, it is preferable todetermine the length “l” of one side of the square shape the glass bulb5 as 200 mm or more, and in this embodiment of the present invention,the above-mentioned length “l” is about 300 mm. The respective ends 5 cof the glass bulbs 5 are closely placed substantially in parallel witheach other, and filament electrodes 8, 8 which are formed of a triplecoil on which emitter material has been applied, are attached to theabove-mentioned respective ends 5 c to form electrode-sealed endportions 5 c.

The electrodes 8, 8 are supported by means of lead wires, which aresupported in a sealed state by means of flare stems, button stems, beadstems or pinch sealing members. Fine tubes for exhausting or fillingmercury alloy may be connected to such stems or members.

Each of the straight tube portions 5 a has a tube inside diameter offrom 12 to 20 mm and a thickness of from 0.8 to 1.5 mm, and in theembodiment of the present invention, the tube inside diameter is ofabout 16 mm and the thickness is of about 1.2 mm. The straight tubeportions 5 a communicate with each other through the bent portions 5 b,and the end portions 5 d, which are placed in opposite to theelectrode-sealed end portions 5 c in the axial directions thereof, areconnected to each other through a connection portion 4 so as tocommunicate with each other to thereby form a single discharge path,which twice surrounds the center “O” of the square shape in a passageextending from one electrode 8 of the inner bulb 2, through theconnection portion 4, to the other electrode 8 of the outer bulb 3. Theconnection portion 4 is formed by applying a burner blast breakingprocess to the connection portion-side end portions 5 d, 5 d of theinner and outer bulbs 2, 3, which are placed on the side of theconnection portion 4.

The inner and outer bulbs 2 and 3 are structured so that the cold spotis generated in at least one bent portion 5 b, or the connectionportion-side end portions 5 d, 5 d, which are furthest apart from theelectrodes 8, 8, when the fluorescent lamp 1 is illuminated. The coldspot is generated in a region of the bulb having the lowest temperature,when the fluorescent lamp 1 is illuminated. Accordingly, the bentportion 5 b may have a structure in which temperature increase is notapt to occur when the fluorescent lamp 1 is illuminated, so as to ensuregeneration of the cold spot. Such a structure is exemplified by forminga space so as to be apart from the discharge path or providing a surfacearea having an excellent heat radiation effect than the other portions.The bent portion 5 b has a smaller surface area ratio relative to thetotal surface area of the bulbs 5, 5 than the straight tube portion 5 a,with the result that a luminescence power is small and its shape can beformed as desired, thus making it possible to easily apply the structurein which temperature increase is not apt to occur to the bent portion.It is therefore possible to easily control the temperature of the coldspot generated in the bent portion 5 b on the basis of the desiredtemperature. Therefore, the optimum pressure of mercury vapor can beensured even at a high ambient temperature, thus permitting a furtherenhancement of luminous efficiency. With the controlling of the pressureof mercury vapor on the basis of the temperature of the cold spot, in analternation, the pressure of mercury vapor may be controlled by means ofamalgam.

The both of the connection portion-side end portions 5 d, 5 d of theinner and outer bulbs 2, 3 are placed to face both the electrode-sealedend portions 5 c, 5 c thereof, respectively, so that the respectiveaxial lines intersect at an angle of about 90 degrees, and a base 9 ismounted so as to straddle a region among these end portions 5 d, 5 d, 5c, 5 c. The base 9 is provided with an incoming device having forexample four pins, which are to be electrically connected to the pair ofelectrodes 8, 8. The base 9 has an electric connection element such asincoming pins, which is to be connected to a power supply device such asa socket. The electric connection element may be provided in a positionapart from the opposite ends of the bulbs 5, 5. The base 9 may have astructure, which enables the base to attain the function as a holdingdevice in a mechanical connection to the power supply device. The bentportions 5 b are provided at three corners of the square shapearrangement, which is formed by the straight tube portions 5 a of eachof the glass bulbs 5, and the base 9 is placed at the remaining onecorner. In FIG. 1, the reference numeral “10” denotes an exhaust pipe.

The fluorescent lamp 1 having the above-described structure isilluminated by the action of a not-shown high frequency lightingcircuit.

The high frequency lighting circuit may be provided with a switchingdevice. The switching device may have a mode in which the fluorescentlamp is illuminated with high efficiency and another mode in which thelamp is illuminated at a high output. The switching device may have afunction of causing a continuous variation between these modes. Aswitching operation of the switching device of the lighting circuitadjusts illuminance of the fluorescent lamp 1. In an example case inwhich the switching device has the high efficiency illuminance mode andthe high output illuminance mode, the fluorescent lamp 1 may be used inan appropriate selection of mode in accordance with conditions of use.

The fluorescent lamp 1 is mounted in compliance with a shape of the mainbody of the lighting apparatus and optical properties thereof. Inaddition, the plurality of fluorescent lamps having the same ordifferent shape are fitted in combination to the main body so that theyare placed on the same plane or at different levels from each other.

The operation of the embodiment of the present invention will bedescribed hereunder.

High frequency voltage is inputted to the base 9 and an arc dischargeoccurs in the path extending from the electrode 8 of the inner bulb 2 tothe electrode 8 of the outer bulb 3 through the connection portion 4,thus causing the fluorescent lamp 1 to be illuminated. When thefluorescent lamp 1 is illuminated, the cold spot is generated in atleast one bent portion 5 b, for example, the bent portion 5 ba, which isfurthest apart from the pair of electrodes 8, 8, or in the connectionportion-side end portion 5 d in the vicinity of the connection portion4. Condition that the temperature of the outer surface of the cold spotis within the range of, for example, from about 40 to 65° C. suffices.Maintenance of the temperature of the cooled zone within theabove-mentioned range can provide the optimum pressure of mercury vaporfor the fluorescent lamp 1, thus permitting illuminance with highluminous efficiency.

According to the fluorescent lamp 1 of the present invention, thedischarge path of the inner bulb 2 is connected to the discharge path ofthe outer bulb 3 to form a single discharge path. It is thereforepossible to extend about twice the discharge path of the wholefluorescent lamp, in comparison with the inner and outer bulbs 2, 3provided in the form of a single tube and enhance about twice the totalluminous flux, thus enhancing the luminous efficiency. In addition,according to the fluorescent lamp 1, after the phosphor layer 7 has beenformed on the inner surface of the glass bulb 5, only thebent-portion-formation prearrangement portion, on which the connectionportion is to be formed, is subjected to a local heating. It istherefore possible to restrain deterioration of phosphor caused by heat,enhance the initial luminous flux and improve the luminous fluxmaintenance factor.

In the embodiment of the present invention, the glass bulb 5 of each ofthe inner and outer bulbs 2, 3 is formed into a square shape bypartially or locally binding the single elongated straight bulb.However, each of the glass bulb 5 may be prepared by connecting aplurality of straight tube bulbs to form bent portions 5 b. In addition,the glass bulb may be formed into a rectangular shape. In an examplecase, the end portions of the plurality of straight tube bulbs may bepartially heated, melted and then subjected to a blast breaking to formconnection portions, and the thus formed connection portions may bethereafter connected to each other and subjected to a molding formationprocess to form bent portions 5 b having the desired shape.

Incidentally, there can be used the glass bulb 5 for each of the innerand outer bulbs 2 and 3, which is substantially free from lead elementand has a sodium oxide content of 1.0 vol. % or less and a softeningtemperature of 720° C. or less. Herein, the phrase “substantially freefrom lead element” means that the incidental impurities may be includedat a certain amount, and preferably of 0.1 vol. % or less. In the mostpreferable case, it is needless to say that glass contains no leadelement.

The phrase “has a sodium oxide content of 1.0 vol. % or less” also meansthat the glass contains no sodium oxide. The reason why the sodium oxidecontent is determined to be 0.1 vol. % or less is that, with the sodiumoxide content exceeding the above-mentioned value, the sodium elementdeposited on the inner surface of the glass bulb 5 may exert aninfluence on the luminous power of the fluorescent lamp 1. Glass, whichis substantially free from lead element and has the sodium oxide contentof 1.0 vol. % or less and the softening temperature of 720° C. or less,can be obtained by adjusting the contents of K₂O and Li₂O and thecontents of CaO, MgO, BaO and SrO. Herein, the softening temperature isa temperature at which a relational expression of viscosity “η” of glass=10^(7.65) dPa·s is satisfied.

With the sodium oxide content of glass bulb 5 of over 0.1 vol. %, sodiumis deposited in the form of an alkaline element on the inner surface ofthe glass bulb 5 during illuminance. Deposition of sodium on the innersurface of the glass bulb 5 causes sodium to react with mercury vaporcharged in the glass bulb 5 to bring about a colored glass bulb 5, thusdeteriorating visible light transmittance, or causes sodium to reactwith phosphor substance in the phosphor layer 7 to bring aboutdeterioration of the phosphor substance, thus decreasing power ofvisible light. Particularly, soda lime glass as conventionally usedcontains sodium oxide of from 15 to 17 vol. %, resulting in severedecrease in power of visible light.

In view of these facts, when the phosphor layer is formed throughapplication on the straight tube bulb, which is formed of glass havingthe sodium oxide content of 1.0 vol. % or less and the softeningtemperature of 720° C. or less, for example of 692° C., and then thebent portions are formed, an amount of sodium deposited on the innersurface of the bulb can be remarkably reduced, thus leading to aneffective restraint on the decreasing in power of visible light causedby the reaction of the sodium. In addition, the softening temperature of720° C. or less leads to a lower heating temperature during a bentportion formation process and restraint on deterioration of thesurrounding phosphor layer caused by heat, thus enhancing the luminouspower.

Each of the glass bulbs 5 used in the embodiment of the presentinvention has the following chemical composition:

SiO 65.0 vol. %, Al₂O₃ 4.0 vol. %, Na₂O 0.05 vol. %, K₂O 11.0 vol. %,Li₂O₃ 2.8 vol. %, CaO 2.0 vol. %, MgO 1.4 vol. %, SrO 5.0 vol. %, BaO8.5 vol. %, SO₃ 0.15 vol. %, B₂O₃ 0 vol. %, Sb₂O₃ 0 vol. %, Fe₂O₃ 0.03vol. %, and the balance 0.17 vol., and the softening temperature is 692°C.

FIG. 2 is a front view of the fluorescent lamp 1A according to thesecond embodiment of the present invention. The fluorescent lamp 1A ischaracterized in that each of the inner and outer bulbs 2 and 3 isformed by connecting five straight tube bulbs to each other so as toform four bent portions 5 b, in the above-described fluorescent lamp 1.

More specifically, in the inner and outer bulbs 2 and 3, one side of thesquare shape of the respective glass bulb 5 is composed of straight tubeportions 5 a a, 5 a a each having a half length of the other sidethereof, a pair of electrodes 8, 8 are provided on the end portions ofthe straight tube portions 5 aa, 5 aa, respectively, to form theelectrode-sealed end portions 5 c, 5 c, and on the other hand, the otherend portions thereof are provided as the connection portion-side endportions 5 d, 5 d, respectively. The base 9 is mounted so as to straddlea region among both the electrode-sealed end portions 5 c, 5 c and boththe connection portion-side end portions 5 d, 5 d. According to theembodiment of the present invention, the base 9 is placed almost in themiddle of the one side of the square shape of the glass bulb 5 so thatthe respective opposite ends of the inner and outer bulbs 2 and 3 faceeach other in the respective same line, thus providing an easy mountingstructure of the base 9.

FIG. 3 is a front view of the fluorescent lamp 1B according to the thirdembodiment of the present invention. The fluorescent lamp 1B ischaracterized in that, in the above-described fluorescent lamp 1, theinner and outer bulbs 2 and 3 are connected to each other throughsupporting members 11, which are placed in respective spaces between thebent portions 5 b of the inner bulb 2 and the corresponding bentportions 5 b of the outer bulb 3, in the form of, for example, acushioning member which has a desired shape such as an elliptic shape inits front view and a heat radiating property and elasticity, and thatthe length “Lc” of the connection portion-side end portion 5 d betweenthe outer end of the connection portion 4 (i.e., the right-hand endsurface in FIG. 3) provided on the inner and outer bulbs 2 and 3 and theend surface of the connection portion-side end portion is set to be 11mm or less. The remaining structural features are identical to those ofthe second embodiment as shown in FIG. 2.

The supporting member 11, which is an adhesive agent thermallyconductive to the extent that heat radiation effect can be provided andmade of, for example, silicone resin, connects the outer surface of eachof the bent portions 5 b of the inner glass bulb 2 to the inner surfaceof each of the bent portions 5 b of the outer glass bulb 3 to hold themtogether into a united body and elastically supports these bulbs by theaction of its elasticity. Accordingly, the strength of the inner andouter bulbs 2 and 3 made of glass can be enhanced.

Firm connection of the inner and outer bulbs 2 and 3 into the unitedbody enables a person to handle these inner and outer bulbs 2 and 3,thus permitting an easy operation of mounting bulbs to the lightingapparatus. In addition, each of the supporting members 11 has the heatradiating property, thus permitting generation of the cold spot “ca” inthe bent portion 5 ba, which is furthest apart from the electrode 8 ofthe outer bulb 3.

Because of the above-reason, it is not necessary to generate the coldspot in the both of the non-luminous connection portion-side endportions 5 d, 5 d. In addition, the end portions 5 d, 5 d have nogrooves for a bulb chuck (by which the bulb is grasped) in the differentmanner from the conventional double-circular fluorescent lamp and areclosed hermetically by means of fusion cutting, thus permitting adecreased length “Lc” of the connection portion-side end portion 5 d.Therefore, the decreased length of the connection portion-side endportion 5 d, which is non-luminous, makes it possible to reduce the darkarea and expand the luminescent area accordingly, thus enhancing thetotal luminous flux.

FIG. 4 is a front view of the fluorescent lamp 1C according to thefourth embodiment of the present invention. The fluorescent lamp 1C ischaracterized in that the gap “Ld” between the outer end surface 5 co ofthe electrode-sealed end portion 5 c in the axial direction thereof andthe outer end surface 5 do of the connection portion-side end portion 5d in the axial direction thereof is decreased, in the above-describedfluorescent lamp 1B. The remaining structural features are identical tothose of the fluorescent lamp 1B as shown in FIG. 3.

More specifically, in the conventional double-circular fluorescent lamp321 as shown in FIG. 21, the electrode-sealed end portions 327 and 328and the end portions on the side of the connection portion 324 arecurved as mentioned above, with the result that gaps “La” and “Lb” onthe inner peripheral side and the outer peripheral side between the endsurfaces 327 a and 328 a of the electrode-sealed end portions 327 and328 and the opposing outer end surfaces 329 a and 330 a on the side ofthe connection portion 324 expand in a trapezoidal shape, and there islimitation in reduction of the gaps.

To the contrary, in the embodiment as shown in FIG. 4, both of the innerand outer electrode-sealed end portions 5 c, 5 c and both of theconnection portion-side end portions 5 d, 5 d are straight and notcurved, with the result that both the outer end surfaces 5 co, 5 co ofthe electrode-sealed end portions 5 c, 5 c can be placed on the sameplane, and namely, so as to be substantially flush with each other, andboth the outer end surfaces 5 do, 5 do of the connection portion-sideend portions 5 d, 5 d can also be placed on the same plane, and namely,so as to be substantially flush with each other.

It is therefore possible to make the inner and outer gaps “Ld”substantially equal to each other between both the outer end surfaces 5co, 5 co of the inner and outer electrode-sealed end portions 5 c, 5 cand both the outer end surfaces 5 do, 5 do of the connectionportion-side end portions 5 d, 5 d, thus permitting reduction of theabove-mentioned gaps “Ld”.

This makes it possible to place the inner and outer electrode-sealed endportions 5 c, 5 c and the connection portion-side end portions 5 d, 5 din the non-luminous areas, so as to be close to each other by thereduced length of the inner and outer gaps “Ld”. Accordingly, the darkareas can be reduced by an approaching length of the end portions, andthe luminescent areas can be expanded, thus enhancing the luminousefficiency.

FIG. 5 is a front view of the fluorescent lamp 1D according to the fifthembodiment of the present invention. The fluorescent lamp 1D ischaracterized in that, in the above-described fluorescent lamp 1according to the first embodiment as shown in FIG. 1, the inner andouter bulbs 2, 3 are connected, at the inner and outer bent portions 5b, 5 b thereof which are placed in opposite to the base 9 in thediagonal direction, to each other through the above-described supportingmember 11 in the form of a united body and these bulbs are elasticallysupported to each other. The sealed portions formed by means of fusioncutting on the connection portion-side end portions 5 d, 5 d have ahemispherical shape. The remaining structural features are identical tothose of the first embodiment.

According to the fluorescent lamp 1D, the base 9 is mounted on both theelectrode-sealed end portions 5 c, 5 c of the inner and outer bulbs 2and 3 and the connection portion-side end portions 5 d, 5 d so as tostraddle a region among these end portions, to provide a united body,thus increasing the strength of the inner and outer bulbs 2 and 3. Inaddition, the inner and outer bent portions 5 b, 5 b placed on the sideopposite to the base 9 in the diagonal direction are connected to eachother through the supporting member 11 and these portions areelastically supported to each other, thus increasing the strength of theinner and outer bulbs 2 and 3.

In addition, only one supporting member 11, which is to be provided onthe bent portions 5 b of the inner and outer bulbs 2 and 3, suffices,thus permitting reduction of material used for the supporting member 11and its cost, as well as an easy fitting operation. The supportingmember 11 may be provided between the straight tube portions 5 a, 5 a.

FIG. 6 is a front view of the fluorescent lamp 1E according to the sixthembodiment of the present invention. The fluorescent lamp 1E ischaracterized in that, in the above-described fluorescent lamp 1Caccording to the fourth embodiment as shown in FIG. 4, theelectrode-sealed end portions 5 c, 5 c are extended linearly toward therespective connection portion-side end portions 5 d, 5 d to formextended portions 5 e, 5 e so that the pair of electrodes 8, 8 is placedin the base 9 so as to be concealed by it. Each of the bent portions 5 bof the outer bulb 3 at the corners thereof has an arc shape “R”. Theremaining structural features are identical to those of the fluorescentlamp 1C according to the fourth embodiment.

More specifically, the lengths of the inner and outer bulbs 2, 3 of thefluorescent lamp 1E are determined so as to satisfy the followingexpression (1):L1>L2, andL3>L4,wherein,

-   L1: the outside length of the right-hand side “mo”, as shown in FIG.    6, of one side of the outer bulb 3, having the electrode 8,-   L2: the outside length of the left-hand side “ho”, as shown in FIG.    6, of one side of the outer bulb 3, having the connection portion 4,-   L3: the outside length of the right-hand side “mi”, as shown in FIG.    6, of one side of the inner bulb 2, having the electrode 8,-   L4: the outside length of the left-hand side “hi”, as shown in FIG.    6, of one side of the inner bulb 2, having the connection portion 4,    to form the extended portions 5 e, 5 e of the pair of    electrode-sealed end portions 5 c, 5 c, thus placing the pair of    electrodes 8, 8 in the base 9 to conceal them therein.

According to the fluorescent lamp 1E of the present invention, the totallength of the outer bulb 3 is extended by the length of the extendedportion 5 e, thus making it possible to increase the length of thedischarge path. The fluorescent lamp 1E can therefore achieve anenhanced luminosity.

In addition, the pair of electrodes 8, 8 are placed in the base 9 toconceal them therein, thus making it possible to conceal shade of theseelectrodes in the base 9. Therefore, the fluorescent lamp 1E can achievethe further enhanced luminosity and an improved external appearance.

The respective lengths L1, L3 of the right-hand sides “mo”, “mi” of therespective one sides of the inner and outer bulbs 2, 3, having the base9 (i.e., the bottom side of the square shape in FIG. 6), as well as therespective lengths L2, L4 of the corresponding left-hand sides “ho”,“hi” are determined so as to satisfy the above-mentioned expression (1),thus making it possible to place the center 9 o of the base 9 in itstransverse direction (i.e., the horizontal direction in FIG. 6) on thecentral line Oa passing through the center “O” of the square shape.

Accordingly, the balance between the left and right-hand sides in weightrelative to the central line Oa can be kept, thus making it possible toimprove an easy handling performance when the fluorescent lamp 1E ismounted on a lighting apparatus, not show, and further improve theexternal appearance.

FIG. 7 is a front view of the fluorescent lamp 1F according to theseventh embodiment of the present invention. The fluorescent lamp 1F ischaracterized in that extended portions 5 f, 5 f, amalgam 12 and asupporting member 11 are provided in addition to the fluorescent lamp 1shown in FIG. 1.

The extended portions 5 f, 5 f are formed by extending linearly the pairof electrode-sealed end portions 5 c, 5 c of the inner and outer bulbs2, 3 so as to place their outer end surfaces in the respective axiallines thereof onto an extended line from the outer surface “a” (i.e.,the bottom surface in FIG. 7) of the connection portion-side end portion5 d of the outer bulb 3, or in the vicinity of the above-mentionedextended line.

The amalgam 12, which is a metallic layer formed of indium (In) or gold(Au) on a substrate made of stainless steel and apt to adsorb mercury,is disposed in the connection portion-side end portion 5 d of the innerbulb 2, which is located in the vicinity of the connection portion 4.The amalgam 12 is supported by means of supporting line 12 a at its oneend and the other end of the supporting line 12 a is connected to theinner surface of the connection portion-side end portion 5 d in a sealedmanner. The amalgam may be mounted by means of flare stem, not shown. Incomparison with a common case in which such a kind of fluorescent lamp1F has a small tube diameter, resulting in a low diffusion velocity ofmercury in the tube and leading to a possible problem of a lowerbuild-up performance of the luminous flux, the amalgam 12 disposedapproximately in the intermediate portion of the discharge path releasesmercury immediately after the illumination, thus achieving theimprovement in the build-up performance of the luminous flux.

The supporting member 11, which is an adhesive agent made of siliconeresin in the same manner as that for the supporting member 11 shown inFIG. 3, is disposed between the outer surface of the connectionportion-side end portion 5 d of the inner bulb 2 and the adjacent outersurface of the electrode-sealed end portion 5 c of the inner bulb 2 toelastically connect them to each other so as to provide a heat radiationfunction. This increases the mechanical strength of the inner bulb 2,thus leading to increase in mechanical strength of the whole fluorescentlamp 1F. In addition, each of the bent portions 5 b of the inner andouter bulbs 2, 3 at their outside surfaces thereof have an arc shape“R”.

The symbol “l”, which denotes the minimum length between the connectionportion 4 and the outer surfaces of the pair of connection portion-sideend portions 5 d, 5 d, is 8 mm in the embodiment of the presentinvention. This length “l” should just be 15 mm or less (within therange of from 0 to 15 mm). It is preferably within the range of from 0to 10 mm, but may be within the range of from 2 to 10 mm.

FIG. 8 is a front view of the fluorescent lamp 1G according to theeighth embodiment of the present invention. The fluorescent lamp 1G ischaracterized in that, in the fluorescent lamp 1F shown in FIG. 7, theamalgam 12, its supporting line 12 a and the supporting member 11 areomitted, and the connection portion 4 is provided in the form of aU-shaped connection portion 4 a, the electrode 8 of the outer bulb 3 isstructured as a so-called high-mount type electrode 8 a, which is placedin a higher position than the electrode 8 of the inner bulb 2, and thebase 9 a is provided so as to entirely conceal the electrodes 8, 8 a.

The U-shaped connection portion 4 a is formed into a U-shape structureintegrally with the inner and outer bulbs 2 and 3 by carrying out, forexample, a molding process, to the connection portion-side end portions5 d, 5 d of the inner and outer bulbs 2 and 3. The length “l” betweenthe outer end (i.e., the right-hand end in FIG. 7) of the connectionportion 4 and the outer surfaces of the pair of connection portion-sideend portions 5 d, 5 d is set to “zero” so as to provide a flat surface.

As a result, the discharge path can be formed also in the U-shapedconnection portion 4 a so that the U-shaped connection portion 4 a isalso illuminated, thus enhancing the luminous efficiency. The flatsurface of the U-shaped connection portion 4 a at the outer end in itsaxial direction does not cause any problem in the process of forming theinner and outer bulbs 2 and 3 into the square shape, since there is noneed to grasp the outer surface of the U-shaped connection portion 4 awith the use of a chuck to form the respective bent portions 5 b of theinner and outer bulb 2 and 3.

The electrode of the outer bulb 3 is structured as the high-mount typeelectrode 8 a, thus enabling the cold spot 13 to be generated at a outercorner on the bottom surface of the electrode end 5 c of the outer bulb3, which is placed in a position lower than the high-mount typeelectrode 8 a in FIG. 8.

Since the above-mentioned cold spot 13 is surrounded with the base 9 a,it becomes possible to improve the stability of temperature, incomparison with the case in which the cold spot is generated at thelower corner of the U-shaped connection portion 4 a in FIG. 8. Morespecifically, the cold spot is exposed directly to an ambient air in thelatter case, thus providing a lower stability in temperature. When thetemperature in the base 9 a is relatively high and the temperature ofthe cold spot is also higher than a standard value, ventilating holesmay be formed in the base 9 a for ventilating the ambient air.

In addition, the electrode of the outer bulb 3 is structured as thehigh-mount type electrode 8 a, resulting in a visual recognition as ifthe luminous area located above the high-mount type electrode 8 a inFIG. 8, is combined together with the luminous area located above theelectrode 8 of the inner bulb 3 and the adjacent luminous area of theU-shaped connection portion 4 a so as to be continuously connected inthe form of arc, thus improving external appearance.

FIG. 9 is a front view of the fluorescent lamp 1H according to the ninthembodiment of the present invention. The fluorescent lamp 1H ischaracterized in that, in the fluorescent lamp 1G shown in FIG. 9, thebase 9 a has a space “S” formed therein, the high-mount type electrode 8a of the outer bulb 3 is changed to the same type as the electrode 8 ofthe inner bulb 2, which is not a high-mount type, and four base pins 14,14, 14, 14 serving as electricity receiving members are provided on theouter surface of the base 9 a above the space “S”.

More specifically, the space “S” in the base 9 a is formed, byshortening the electrode-sealed end portion 5 c of the outer bulb 3relative to the electrode-sealed end portions 5 c of the inner bulb 2,so as to be placed outside the electrode-sealed end portions 5 c of theouter bulb 3 in the axial direction thereof.

The base 9 a located above the space “S” is provided on its outersurface with, for example, four base pins 14. Each of the base pins 14passes through the base 9 a from the outer surface thereof to the innersurface thereof. The inner ends of these pins are connected to innerlead wires 16 of the electrodes 8, 8 through outer lead wires. The base9 a is formed of resin, for example, into a hollow prism shape through amolding formation process. The base is composed of at least two dividedsections, which correspond to the front and back surfaces of a sheet ofpaper of FIG. 9.

According to the fluorescent lamp 1H of the present invention, the fourouter lead wires 15 can be connected to the respective inner ends of thefour base pins 14 in the space “S” within the base 9 a so as to ensure aspace for routing appropriately the outer lead wires 15. It is thereforepossible to improve easiness of connecting and wiring operation andprevent interference between these outer lead wires 15, respectively.

FIG. 10 is a front view of the fluorescent lamp 1I according to thetenth embodiment of the present invention. FIG. 11 provides, at itsupper section, a partial end view of the inner and outer bulbs 2, 3, inwhich the connection portions 4 thereof have not yet been connected toeach other, and also provides, at its lower section, a partial end viewof the inner and outer bulbs 2, 3, in which the connection portions 4thereof have already been connected to each other. The end view on theright-hand side in FIG. 11 provides a view based on the viewing lineXIA-XIA in FIG. 10 and the end view on the right-hand side in FIG. 11, aview based on the viewing line XIB-XIB in FIG. 10. The fluorescent lamp11 is characterized in that, in the fluorescent lamp 1A shown in FIG. 2,there is improved a pair of discharge pipes 16 a, 16 b of the respectiveinner and outer bulbs 2, 3, each of which is formed of an L-shaped glasspipe, not shown.

More specifically, one of the inner and outer bulbs 2, 3, for example,the inner bulb 2, is slightly shortened so that the outer end surface ofthe electrode-sealed end portion 5 c of the inner bulb 2 is slightlyshifted outwardly (i.e., toward the right-hand side in FIG. 10) from theouter end surface of the electrode-sealed end portion 5 c of the outerbulb 3. A pair of discharge pipes 16 a, 16 a are provided on therespective outer surfaces of the electrode-sealed end portions 5 c, 5 cof the inner and outer bulbs 2 and 3 so as to project outward in theaxial direction thereof. The discharge pipes, which communicate with therespective insides of the inner and outer bulbs 2 and 3, are connectedat their outer opening ends to a head of a supplying and dischargingunit, not shown, so as to discharge the air from the inner and outerbulbs 2, 3 and to supply rare gas such as argon and mercury therein.

As shown in FIG. 11, one of the paired discharge pipes 16 a, 16 b, forexample, the discharge pipe 16 a, projects slightly outward from theouter end surface of the electrode-sealed end portion 5 c of the innerbulb 2 so as to be concentric therewith in the axial direction (i.e. thehorizontal direction), curves in the form of arc and then extends upwardin the perpendicular direction to the axial direction (i.e., thevertical direction).

To the contrary, the other discharge pipe 16 b projects slightly outwardfrom the outer end surface of the electrode-sealed end portion 5 c ofthe outer bulb 3 so as to be concentric therewith in the axial direction(i.e. the horizontal direction), curves in the form of arc and thenextends downward in the perpendicular direction to the axial direction(i.e., the vertical direction).

The paired discharge pipes 16 a, 16 b face in the opposite directions toeach other (i.e., the upward and downward directions) in theperpendicular direction to the axial direction of the inner and outerbulbs 2 and 3. Even when the pair of discharge pipes 16 a, 16 b areplaced close to each other, it is possible to connect easily and rapidlythe above-mentioned discharging and supplying head to the outer openingend of the other discharge pipe, e.g., the pipe 16 a in a reliablemanner, without interruption or hindrance by one of them (for example,the pipe 16 b).

In the case where a pair of discharging and supplying heads areprovided, it is possible to connect substantially simultaneously theseheads to the discharge pipes 16 a, 16 a so as to conduct a dischargingand supplying operation, thus permitting an improved operationalefficiency of the discharging and supplying process.

Upon connection of the connection portions 4 of the inner and outerbulbs 2 and 3 as shown in FIG. 11, the portions, on which the connectionportions 4 are to be formed, of the paired upper and lower connectionportion-side end portions 5 d, 5 d are heated to be softened by a flamefrom a burner, while blasting gas having a predetermined pressure intothe bulbs from the paired upper and lower discharge pipes 16 a, 16 b tobreak, by blast, the softened portions, on which the connection portions4 are to be formed, and fusion-connecting the tip ends as broken, whichproject outward. The connection portion 4 is formed in this manner, asshown in the lower and left-hand side of FIG. 11.

It is possible to connect the pair of upper and lower discharging andsupplying heads to the pair of discharge pipes 16 a, 16 b to carry out agas blowing process also in the case of forming the connection portion4, thus advancing simply and rapidly the formation process of theconnection portion 4 in a reliable manner and improving the operationefficiency.

The pair of discharge pipes 16 a, 16 b are to be cut with their cut rootends, after completion of the discharging and supplying process and theformation process of the connection portion 4. Each of the bent portions5 b of the inner and outer bulbs 2, 3 at the outside surfaces thereofhas an arc shape “R”.

FIG. 12 is a front view of the fluorescent lamp 1J according to thesixteenth embodiment of the present invention. The fluorescent lamp 1Jis characterized mainly in that, in the fluorescent lamp 11 shown inFIG. 10, the length of the electrode-sealed end portion 5 c of the outerbulb 2 is shorten relative to the length of the electrode-sealed endportion 5 c of the inner bulb 2, and a pair of upper and lower dischargepipes 16 a, 16 b are substituted with a pair of inner and outerdischarge outward pipes 16 a, 16 b, which face outward relative to thecenter “O” of the square shape structure. The remaining structuralfeatures are substantially similar to those of the fluorescent lamp 1I.

More specifically, the length of the side corresponding theelectrode-sealed end portion 5 c of the inner bulb 3 is shortened sothat the outer end surface of the electrode-sealed end portion 5 c ofthe outer bulb 3 is slightly shifted inwardly (i.e., toward theright-hand side in FIG. 12) from the outer end surface of theelectrode-sealed end portion 5 c of the inner bulb 2, so as to form apassage through which the inner discharge pipe 16 c of the inner bulb 2passes outside the rectangular shape.

The paired outward discharge pipes 16 c, 16 d slightly project outwardfrom the outer end surfaces of the pair of inner and outerelectrode-sealed end portions 5 c, 5 c in their axial directions (i.e.,the horizontal direction), curve in the form of arc and then extendoutside the fluorescent lamp 1J in parallel with each other.

FIGS. 13 to 15 show the fluorescent lamp 101 according to the twelfthembodiment of the present invention, and FIG. 13 is a schematic frontview of the fluorescent lamp 101, partially broken away, FIG. 14 is aschematic front view of the fluorescent lamp 101 provided with a base,and FIG. 15 is a schematic block diagram of a high frequency lightingdevice 116.

As shown in FIG. 13, the fluorescent lamp 101 is composed of thedouble-circular structure glass bulb 102, which is structured in thesimilar manner as the second embodiment as shown in FIG. 2, a pair offirst electrodes 103, 103, a second electrode 104, and a phosphor layer105.

The glass bulb 102 is structured in the form of double-ring (doublebulb) by disposing the outer bulb 107 on the outside of the inner bulb106 on the same plane so as to be concentric with each other at apredetermined gap “g” and connecting them through the connection portion108 to form a single discharge path.

The inner bulb 106 has five straight tube portions 106A1 to 106A5 andfour bent portions 106B so that the opposite ends 106 a, 106 b face eachother. The outer bulb 107 has five straight tube portions 107A1 to 107A5and four bent portions 107B so that the opposite ends 107 a, 107 b faceeach other.

The first electrode 103, which is a hot cathode type filament electrodeon which an emitter is applied, is placed in each of the other endportions (i.e., the end portions of the bulbs 102, which are placed onthe opposite side to the connection portion 108) of the inner bulb 106and the inner bulb 107. The second electrode 104, which has the samestructure as the first electrode 103, is placed in the one end portion(i.e., the end portion of the of the outer bulb 107, on which theconnection portion 108 is formed) of the outer bulb 107. The one endportion 106 a of the inner bulb 106 is air-tightly closed by applying afusion cutting process or attaching a sealing member such as a dummystem. The bulb ends 106 b, 107 b are located at the opposite ends of thesingle discharge path formed in the bulb 102, respectively, and the bulbend 107 a in which the second electrode 104 is disposed, is located atthe intermediate portion of the above-mentioned discharge path.

The first electrodes 103, 103 and the second electrode 104 are filamentelectrodes formed of a triple coil on which emitter material has beenapplied. The opposite ends of each of these electrodes are supported bymeans of a pair of lead wires 109, 109. These lead wires 109, 109 aresupported in a sealed state by means of flare stems 110, which arefitted into the other end portion 106 b of the inner bulb 106 and theopposite end portions 107 a, 107 b of the outer bulb 107, so as toproject outward. In the accompanying figures, the reference numeral“105” denotes a phosphor layer, which is formed on the protection layer,not shown, and includes three-band fluorescent type phosphor particles.

The base 111 having an approximately rectangular parallelepiped isattached to the respective opposite ends 106 a, 106 b, 107 a, 107 b ofthe inner bulb 106 and the outer bulb 107 so as to straddle a spacebetween these ends 106 a, 106 b, 107 a, 107 b, as shown in FIG. 14. Anelectric cable 112 extends from the base 111, and a connector 114, whichhas, at its tip end, six connection pins 113, is connected to theleading end of the electric cable 112. Each of the connection pins 113is electrically connected to the lead wires 109, 109 of the bulb 102through the electric cable 112. The connection pins 113 may be embeddedon the outer surface of the base 111, without being connected throughthe electric cable 112 and the connector 114.

Supporting members 115 each of which is made of silicone resin, areprovided between the inner bulb 106 and the outer bulb 107.

The fluorescent lamp 101 is connected to the high frequency lightingdevice 116, as shown in FIG. 15. The high frequency lighting device 116is composed of output terminals 116 a, 116 b, 116 c, 116 d, a knowndirect voltage generation circuit 117, a main circuit 118 and a controlcircuit 119. The direct voltage generation circuit 117, which includesfor example a rectifier instrument and a smoothing capacitor (both ofthem are not shown), rectifies and smoothes alternating voltage from acommercial alternating-current power supply Vs to generate currentvoltage. The main circuit 118, which includes a switching element, notshown, such as a field-effect transistor, converts the current voltageoutputted from the direct voltage generation circuit 117 into highfrequency voltage through a switching operation of the switchingelement, and outputs the high frequency voltage to the output terminals16 a -116 d.

Connection of the connector 114 of the fluorescent lamp 101 to theoutput terminals 16 a -116 d leads to connection of the opposite ends ofthe first electrode 103 at the side of the other end portion 107 b ofthe outer bulb 107 to the output terminals 116 a, 116 a, and connectionof the opposite ends of the first electrode 103 at the side of the otherend portion 106 b of the inner bulb 106 to the output terminals 116 b,116 b, and connection of the opposite ends of the second electrode 104at the side of the one end portion 107 a of the outer bulb 107 to theoutput terminals 116 d, 116 d. In FIG. 15, the base 111, the connectionpins 113 and the connector 114 as shown in FIG. 14 are omitted.

The control circuit 119 causes the switching element to carry out aswitching operation at a preheating frequency, a starting frequency anda lighting frequency. As a result, a preheating voltage outputted fromthe main circuit 118 is applied between the respective opposite ends ofoutput terminals 116 a, 116 a, the output terminals 116 b, 116 b and theoutput terminals 116 d, 116 d during a preheating period of thefluorescent lamp 101, and the starting voltage and the lighting voltageare applied between the output terminals 116 a, 116 d or the outputterminals 116 a, 116 b when starting and lighting.

In addition, it is configured that the above-mentioned output voltageoutputted from the main circuit 118 is supplied to the output terminals116 b, 116 b through the switch SW1 and to the output terminals 116 d,116 d through the switch SW2. More specifically, when the switch SW1 iskept in an “ON” state, the output voltage from the main circuit 118 isapplied between a pair of first electrodes 103, 103 (to the primarydischarge path), and when the switch SW2 is kept in an “ON” state, theoutput voltage from the main circuit 118 is applied between the firstelectrode 103 and the second electrode of the outer bulb 107 (to thesecondary discharge path). The switches SW1 and SW2, which are kept inan “ON” state, enables the first electrode 103 of the outer bulb 107 tobe used as a common electrode to generate output voltage in the primarydischarge path and the secondary discharge path. The switch SW2, whichis kept in an “OFF” state, disables the output voltage from beingapplied to the secondary discharge path. The control circuit 19 isconfigured so as to permit independent control of the ON-OFF operationof the switches SW1 and SW2.

The operation of the fluorescent lamp 101 according to the twelfthembodiment of the present invention will be described hereunder.

In order to start the lighting of the fluorescent lamp 101 forillumination with the use of the high frequency lighting device 116, theswitches SW1, SW2 are kept first in an “ON” state to output thepreheating voltage from the main circuit 118 so as to preheat a pair offirst electrodes 103, 103 and the second electrode 104.

After the first electrodes 103, 103 and the second electrode 104 havebeen preheated fully, the predetermined starting voltage is applied fromthe main circuit 118 of the high frequency lighting device 116 betweenthe second electrode 104 and the first electrode 103 of the outer bulb7, and between the pair of first electrodes 103, 103 of the illuminationtube 102 (i.e., between the first electrode 103 of the inner bulb 106and the first electrode 103 of the outer bulb 107). At this time, thesecond electrode 104 of the outer bulb 107 and the first electrode 103of the inner bulb 106 have the same electrical potential. The startingvoltage is remarkably higher than the lamp voltage of the illuminationtube 102 during the normal lighting mode.

The starting voltage is applied between the second electrode 104 of theouter bulb 107 and the first electrode 103 as well as between the firstelectrodes 103, 103 of the illumination tube 102 at the same voltagevalue, with the result that discharge is generated in the secondarydischarge path (i.e., between the second electrode 104 and the firstelectrode 103 of the outer bulb 107), which has a smaller length thanthe primary discharge path of the illumination tube 102, thus providingillumination of the outer bulb 107. A not-shown detecting device may beprovided to detect the illumination of the outer bulb 107. The controlcircuit 119 causes only the switch SW2 to be kept in an “OFF” state, atthe time when the detection by the detecting device is made, or after alapse of the predetermined period of time from the start of applicationof the starting voltage.

The voltage having the same electrical potential as the second electrode104 is applied to the first electrode 103 of the inner bulb 106.Accordingly, when the switch SW2 is kept in an “OFF” state, the end ofthe discharge occurring in the secondary discharge path in the outerbulb 107 extends from the second electrode 104 to the first electrode103 of the inner bulb 106, thus entering the discharge mode utilizingthe primary discharge path between the first electrodes 103, 103 of theillumination tube 102. Subsequently, the fluorescent lamp 101 isilluminated at high frequency in a stable manner.

In the fluorescent lamp 101, the discharge occurs in the primarydischarge path after the discharge occurs in the secondary dischargepath having the shorter length of the primary discharge path, with theresult that a voltage, which is comparable to the voltage required forthe start of lighting of the outer bulb 10, could be applied in the formof starting voltage, thus making it possible to reduce the startingvoltage for the fluorescent lamp 101, in comparison with application ofthe starting voltage only between the paired electrodes 103, 103 of theillumination tube 102, and permitting an easy design of circuit of thehigh frequency lighting device 116.

Alternatively, it is possible to keep the switch SW1 in an “OFF” stateand the switch SW2 in an “ON” state to generate consecutively theprimary discharge between the first electrode 103 and the secondelectrode 104 of the outer bulb 107 (i.e., in the secondary dischargepath) so as to cause only the outer bulb 107 to be illuminated, thuspermitting the selection of the bulb to be illuminated in thefluorescent lamp 101.

Hereunder, the fluorescent lamp according to the thirteenth embodimentof the present invention will be described. In this fluorescent lamp,the second electrode 104 is provided at the one end portion 106 a of theinner bulb 106, in place of the one end portion 107 a of the outer bulb107 of the fluorescent lamp 101 as shown in FIG. 13. The remainingstructural features are identical to those of the twelfth embodiment ofthe present invention, and detailed description thereof is thereforeomitted.

FIG. 16 is a schematic front view of the fluorescent lamp 121, partiallybroken away, according to the fourteenth embodiment of the presentinvention. The same reference numerals are given to the same componentsas those in FIG. 13, and the description relevant thereto will beomitted herein.

The fluorescent lamp 121 has a structure as shown in FIG. 16 in whichthe second electrode 104 is additionally provided at the one end portion106 a of the inner bulb 106, in the fluorescent lamp 101 as shown inFIG. 13.

The fluorescent lamp 121 is connected to the high frequency lightingdevice 122 shown in FIG. 16. More specifically, the output terminals 116a, 116 a, 116 d, 116 d of the high frequency lighting device 122 areconnected to the respective opposite ends of the first electrode 103 andthe second electrode 104 of the outer bulb 107, and the output terminals116 b, 116 b, 116 c, 116 c are connected to the respective opposite endsof the first electrode 103 and the second electrode 104 of the innerbulb 106. Switches SW1 to SW4 are disposed between the output terminals116 a to 116 d and the main circuit 118 of the high frequency lightingdevice 122. With respect to the other structural features of the highfrequency lighting device 122, it has the same structure as the highfrequency lighting device 116 as shown in FIG. 15.

Operation is carried out in the same manner as described and illustratedin FIG. 15 to start the lighting for illumination of the fluorescentlamp 121. More specifically, discharge occurs between the firstelectrode 103 and the second electrode 104 of the outer bulb 107 (i.e.,in the secondary discharge path), with the switches SW1 to SW3 kept inan “On” state and the switch SW4 in an “OFF” state. At this time, theswitching operation has already been carried out by a switch, not shown,in the primary circuit 118 so that the second electrode 104 of the outerbulb 107 and the first electrode 103 of the inner bulb 106 have the sameelectrical potential. Then, the switch SW2 is kept in an “OFF” state togenerate discharge between the pair of first electrodes 103, 103 of theillumination tube 102, thus providing subsequent illumination.

The switches SW1, SW3, SW4 may be kept in an “ON” state to apply thestarting voltage to the secondary discharge path so as to generatedischarge, and then, the switch SW4 may be kept in an “OFF” state togenerate discharge in the primary discharge path in the similar manner.

In the fluorescent lamp 121 according to the embodiment of the presentinvention, the second electrode 104 and the first electrode 103 aredisposed on the opposite end portions 106 a, 106 b of the inner bulb106, respectively, and the second electrode 104 and the first electrode103 are disposed on the opposite end portions 107 a, 10 b of the outerbulb 107, thus making it possible to cause the inner bulb 106 or theouter bulb 107 to be illuminated independently from each other in theform of a single fluorescent lamp. Supply of the high frequency voltagefrom the high frequency lighting device 122, with the switches SW2, SW3kept in an “ON” state, and the switches SW1, SW4 kept in an “OFF” state,generates subsequently the primary discharge between the first electrode103 and the second electrode 104 to illuminate the outer bulb 107.Alternatively, the high frequency voltage is supplied from the highfrequency lighting device 122, with the switches SW1, SW4 kept in an“ON” state, and the switches SW2, SW3 kept in an “OFF” state, andsubsequently, the primary discharge id generated between the firstelectrode 103 and the second electrode 104 to thereby illuminate theinner bulb 106.

Since the inner bulb 106 and the outer bulb 107 are provided withphosphor layers 105, which are different in luminescence color from eachother, color of light radiated from the fluorescent lamp 121 changes.For example, in a case where the inner bulb 106 is provided on its innersurface with the phosphor layer having daylight color, and the outerbulb 107 is provided on its inner surface with the phosphor layer 105having neutral white color, the illumination (luminescence) of the innerbulb 106 enables light having the daylight color to be radiated from thefluorescent lamp 121, the illumination of the outer bulb 107 enableslight having the neutral white color to be radiated from the fluorescentlamp 121, and the illumination of the illumination tube 102 enableslight having the intermediate between the daylight color and the neutralwhite color to be radiated from the fluorescent lamp 121.

In the thirteenth to fifteenth embodiments of the present invention, thesecond electrode 104 may be disposed as an auxiliary electrode forgenerating a discharge for start, without causing the primary dischargeto be generated between the second electrode 104 and the first electrode103. In the case where the second electrode is used as the auxiliaryelectrode, there is no need to use the filament electrode and a merelyconductive body formed of wells or a cold cathode such as a nickelsleeve may be used.

Now, the sixteenth embodiment of the present invention will be describedbelow.

FIG. 17 is a schematic front view of a lighting apparatus 123, partiallybroken away, according to the fifteenth embodiment of the presentinvention. In FIG. 17, the same reference numerals are given to the samecomponents as those in FIGS. 13 to 15 and the description relevantthereto will be omitted herein.

The lighting apparatus 123 as shown in FIG. 17, which is a surfacemounted type with a glove 124 and to be mounted directly on a surfacesuch as a ceiling surface, has a main body 125 is secured on the ceilingsurface by means of screws. The main body 125 is provided with aplurality of lamp holders 126. The fluorescent lamp 101 is mounted onthe main body 125 so that the straight tube portions 106A2, 107A2,—ofthe inner bulb 106 and the outer bulb 107 of the illumination tube 102are supported by the lamp holders 126.

The main body 125 is provided with an adaptor 127. The high frequencylighting device 116 is received in the adaptor 127, which is connectedto an external commercial alternating-current power supply. Connectionpins 113 of the connector 114 are fitted into the adaptor 127 so thatthe high frequency lighting device 116 and the first and secondelectrodes 103, 104 of the fluorescent lamp 101 are connected to eachother.

The high frequency lighting device 116 starts the lighting of thefluorescent lamp 101 at a low starting voltage so that the discharge isgenerated in the primary discharge path after the starting voltage hasbeen applied to the secondary discharge path at the start of lighting ofthe fluorescent lamp 101 to generate discharge therein.

FIG. 18 is a front view of the fluorescent lamp 201 according to thesixteenth embodiment of the present invention. The fluorescent lamp 201includes a double-ringed illumination tube 202 composed of the innerring bulb 202 a and the outer ring bulb 202 b, having the similar shapeto each other so that the straight portions form substantially a squareshape and their maximum ring diameters are different from each other.The ring glass bulbs 202 a, 202 b are connected to each other by meansof a connection pipe 202 c serving as the connection portion, so thatthese bulbs communicate with each other at the predetermined positionsof the end portions thereof. The connection pipe 202 c is formed byfusion-connecting protrusions provided in the form of a tubular body onthe end portions of the bulbs 202 a, 202 b by a blast breaking process.The connection pipe 202 c is formed apart from the ends of the bulbs 202a, 202 b by the length of 2 to 15 mm so as to provide a space in whichno discharge is generated.

Each of the ring glass bulbs 202 a, 20 b has four straight tube portions“S” and three bent portions “C” so that the four straight tube portions“S” are placed on the same plane so as to form the respective sides ofthe square shape structure. It is preferable that the length “La” of oneside of the inner ring bulb 202 a is 200 mm or more, and the length “La”of one side of the outer ring bulb 202 b is 250 mm or more. In theembodiment of the present invention, “La” is about 250 mm, and “LB” isabout 300 mm. It is preferable that the tube inside diameter of thestraight tube portion “S” is within the range of from 12 to 20 mm andthe thickness thereof is within the range of from 0.8 to 1.5 mm. In theembodiment of the present invention, the tube inside diameter is about14 mm and the thickness is about 1.2 mm.

The ring bulbs 202 a, 202 b are combined concentrically to each other sothat the centers thereof are placed in the same position and thecorresponding bent portions “C” face in the same direction so as to awayfrom the respective centers thereof. The ring bulbs 202 a, 202 b areconnected to each other by means of the connection pipe 202 c so thatthe centers of the corresponding bent portions 202 c with radii ofcurvature are placed in substantially the same position.

FIG. 19 is an enlarged front view of a part of the bent portion “C”. Asshown in FIG. 19, the bent portion “C” is formed so that the center ofradius of curvature “r1 a” of the inner surface C1 1 of the inner ringbulb 202 c having the smaller size, the center of radius of curvature“r2 a” of the outer surface C2 a thereof, the center of radius ofcurvature “r1 b” of the inner surface C1 b of the outer ring bulb 202 bhaving the larger size, and the center of radius of curvature “r2 b” ofthe outer surface thereof are placed substantially in the same point“O”. The ring bulbs 202 a, 202 b are connected to each other to form theillumination tube 202.

The fluorescent lamp 201 is structured so that the centers of thecorresponding bent portions “C” with radii of curvature are placed inthe same position in the combination of the ring bulbs 202 a, 202 bhaving the sizes different from each other, thus making it possible tomake a gap “Wc” between the adjacent bent portions “C” substantiallyequal to a gap between the adjacent straight tube portions, andimproving an external appearance of the fluorescent lamp 201. Cushioningmembers made of silicone resin may be provided between the ring bulbs202 a, 202 b to enhance the strength of the ring bulbs 202 a, 202 b. Inthis case, it is possible to limit the gaps “Ws” and “Wc” within therange of from 5.0 to 10.0 mm, taking into consideration the lightradiation efficiency of the illumination tube 202 or productivity of theconnection pipe 202 c.

The bent portion “C” is formed by bending a straight tube bulb and thensubjecting it to a molding formation process. The inner surfaces “C1 a”,“C1 b” of the bent portions “C” mean surfaces, which face to the centerof the imaginary circular curved surfaces formed by the ring bulbs 202a, 202 b. The outer surfaces “C2 a”, “C2 b” of the bent portions “C”mean surfaces, which are located on the side opposite to the innersurfaces “C1 a”, “C1 b” of the bent portions “C” relative to the axialline of the tube by 180 degrees (i.e., surfaces that are radially inparallel with the circular curved surfaces formed by the ring bulbs 202a, 202 b).

The radius of curvature “r1 a”, “r1 b”, “r2 a”, “r2 b” can be defined bya curve, which is formed in a position at which the inner surface “C1a”, “C1 b” or the outer surface “C2 a”, “C2 b” intersects the imaginarycircular curved surface formed by the ring bulb 202. In a simpledetermination, it can be defined by a radius of curvature of an innercontour line or an outer contour line of the bent portion “C”, whenviewing the ring bulb 202 a, 202 b in the perpendicular direction to theimaginary circular curved surface formed by the ring bulb. The optimumrange of the radius of curvature “r1 a” is within the range of from 13to 20 mm, the optimum range of the radius of curvature “r2 a” is withinthe range of from 25 to 45 mm, the optimum range of the radius ofcurvature “r1 b” is within the range of from 30 to 55 mm, and theoptimum range of the radius of curvature “r2 b” is within the range offrom 45 to 70 mm. In the embodiment of the present invention, the radiusof curvature “r1 a” is 15 mm, the radius of curvature “r2 a” is 31.5 mm,the radius of curvature “r1 b” is 40 mm, and the radius of curvature “r2b” is 56.5 mm.

The tube diameter “Dc” of the bent portion “C” is substantiallyidentical to the tube diameter “Ds” of the adjacent straight tubeportion 202 b. Such formation of the bent portions “C” causes a personto visually recognize as if the bent portions “C” of the ring bulbs 202a, 202 b in its external appearance continue from the straight portion“S” to form a curved line. Therefore, an improved external appearance ofthe luminescent lamp 201 can be provided and there is no formation of alocal area having a lower temperature, when illuminating. As a result,the cold spot cannot be generated easily, and the bent portion “C” isnot susceptible to occurrence of blackening or stain due to condensedmercury. In the embodiment of the present invention, both of the tubediameter “Dc” of the bent portion and the tube diameter “Ds” of thestraight tube portion 202 b are 16.5 mm. The length “l” of the straighttube portion “S” is 237 mm.

Hereunder, a method of manufacturing the glass bulbs 202 a, 202 b usedin the fluorescent lamp 201 according to the embodiment of the presentinvention will be described.

First, there is prepared a single straight bulb on which the protectivelayer and the phosphor layer have previously formed. One end of the bulbis closed, and the electrode is disposed in the other end of thestraight tube bulb through a flare stem, which has a discharge pipe andintroduces a pair of lead wires.

The straight tube bulb has the total length of from 1200 to 1500 mm andthree bent-portion-formation prearrangement portions. Each of theseprearrangement portions has the length of about 90 mm, and the totallength of three prearrangement portions 202 e is 270 mm, which is about18 to 23% of the total length of the straight tube bulb 202 a.

The straight bulbs having the length applicable to the shape of each ofthe glass bulbs 202 a, 202 b is heated at the respectivebent-portion-formation prearrangement portions to soften, bent so thatan angle between the straight tube portions is about 90 degrees, andthen subjected to a molding process to form three bent portions havingthe predetermined shape. The glass bulbs 202 a, 202 b are blast-brokenat the predetermined positions of the respective ends thereof to formtubular bodies projecting therefrom and these tubular bodies arefusion-connected to each other so as to from a connection pipe 2 c. Airis discharged from the discharge pipes and then mercury is charged tocomplete the manufacture of the double-ringed fluorescent pipe 202. Insuch a fluorescent pipe 202, the ring bulbs 202 a, 202 b communicatewith each other through the connection pipe 202 c, with the result thata single discharge path having the double-ringed structure in which oneround having a square shape is connected at the one end thereof to theother round.

The bent portion “C” is formed by a bent formation process, but there isno need to excessively heat the other portions of the straight bulb thanthe bent-portion-formation prearrangement portions. Accordingly, evenwhen the phosphor layer is formed through a coating (application)process before the formation of the bent portion “C”, the phosphor layeris not susceptible to thermal deterioration and the luminous fluxmaintenance factor can be improved remarkably, thus providingadvantageous effects. These effects can be remarkably provided when thetotal length of the bent-portion-formation prearrangement portions is upto 50% of the total length of the straight tube bulb, preferably up to30% thereof, and most preferably, up to 20% thereof.

Now, this embodiment of the present invention will operate as follows.

The high frequency voltage is inputted from the base 206 to illuminatethe fluorescent lamp 201 through discharge of mercury vapor having a lowpressure. The fluorescent lamp 201 is illuminate so that the luminousinput power is at least 40 W, the luminous current is at least 200 mA,the tube wall load is at least 0.05 W/cm², and the luminous efficiencyis at least 501 m/W. The luminous electric density, which is theluminous current per cross-section of the straight tube portion 202 b,is at least 75 A/cm². In the embodiment of the present invention, theluminous input power is 60 W, the luminous current is 380 mA and theluminous efficiency is 901 m/W.

The temperature of the bulb 202 increases to about 80° C., when thefluorescent lamp 201 is illuminated. However, the portion of thefluorescent lamp 201, which is shifted from the connection portion 202 ctoward the end side of the lamp, serves as a non-discharge generationzone to generate the cold spot having the optimum temperature.Accordingly, the pressure of mercury vapor in the bulbs 202 a, 202 b iskept proper, thus permitting illumination at the high efficiency.

The specific features of the fluorescent lamp 201 of the presentinvention will be described below. The present inventors have carriedout extensive studies about a balance between the luminous power andformability of the bent portion “C” and obtained findings that it ispreferable that the length “l” of the straight tube portion “S” iswithin the range of from 150 to 500 mm, and the radius of curvature “r1”(r1 a and r1 b) of the inner surfaces C1 a, C1 b of the bent portionsatisfies the relational expression of “0.03≦r1/l≦0.3. With the ratio“r1/l” of the radius of curvature “r1” of the inner surface of the bentportion relative to the length “l” of the straight tube portion “S” ofless than 0.03, a degree of deformation of the bent portion becomeslarge, resulting in the difficulty in manufacture and decrease instrength. On the other hand, with the ratio “r1/l” of over 0.3, theratio of the bent portion relative to the ring bulb increases, resultingin that the influence due to deterioration of the phosphor layer in thebent portion “C” caused by heat becomes large, thus leading to a reducedluminous efficiency. Therefore, such a condition is not acceptable. Inthe fluorescent lamp 201, the length “l” of the straight tube portion“S” of each of the ring bulbs 202 a, 202 b is 237 mm within the range offrom 150 to 500 mm, the radius of curvature “r1 a” of the inner surface“C1 a” of the inner ring bulb 202 a is 15 mm, and the radius ofcurvature “r1 b” of the inner surface “C1 b” of the outer ring bulb 202a is 40 mm. Accordingly, “r1 a/l” is about 0.06 and “r1b/l” is about0.16, which satisfy the above-mentioned relational expression of“0.03≦r/l≦0.3”.

In the fluorescent lamp according to the embodiment of the presentinvention, the centers of the inner surfaces C1 a, C1 b and outersurfaces C2 a, C2 b, having the respective radii of curvature “r1 a”,“r1 b”, “r2 a”, “r2 b”, are placed substantially in the same position,thus making it possible to cause a person to visually recognize as ifthe bent portions “C” of the ring bulbs 202 a, 202 b in their externalappearance continue from the straight tube portion “S” to form a curvedline, thus improving an external appearance of the illumination tube202. In addition, it is possible to make the gap “Wc” between theadjacent bent portions substantially equal to the gap “Ws” between thestraight tube portions and to improve the external appearance incomparison with a case where a plurality of ring bulbs are combinedtogether so as to make the radii of curvature of the inner surfaces ofthe bent portions equal to each other. A uniform brightness can also beprovided.

In addition, the radii of curvature “r1 (r1 a and r1 b)” of the innersurfaces “C1 a, C1 b” of the bent portion “C” satisfy the expression of“0.03≦r/l≦0.3” in the case where the length “l” of the straight tubeportion “S” of the illumination tube 202 is within the range of from 150to 500 mm, thus making it possible to form easily the bent portion “C”and minimize the influence due to the deterioration of the phosphor ofthe bent portion “C”, which is caused by heat, to utilize effectivelythe luminous power from the straight tube portion “S”.

FIG. 20 is a front view of the fluorescent lamp 201A according to theseventeenth embodiment of the present invention. The seventeenthembodiment is identical to the sixteenth embodiment as shown in FIG. 19except that the base 206 is placed in the middle of one side of thesquare shape. Each of the glass bulbs 202 a, 202 b has five straightportions “S” and four bent portions “C”. The base 206 is placed so as tostraddle a space between the respective opposite ends of the ring bulbs202 a, 202 b in which the respective axial lines are aligned with eachother. The base 206 is disposed at the intermediate portion of one sideof each of the bulbs 202 a, 202 b having the square shape.

INDUSTRIAL APPLICABILITY

According to the present invention, each of the inner and outer bulbsare formed by heating a single elongated straight bulb having the innersurface on which layers such as a phosphor layer has previously formedlocally only at bent-portion-formation prearrangement portions, andalternatively, heating only the corresponding ends of a plurality ofstraight bulbs, which are to be connected to form the connectionportion, and the remaining portions of the bulb are not subjected to aheating process. It is therefore possible to control strain caused bythe heating of the whole inner and outer ring bulbs, and increase thestrength.

Even in the case where the connection portion is formed by subjectingthe corresponding one ends of the inner and outer bulbs through a burnerblast breaking process, the inner and outer bulbs generally have lowstrain controlled as described above, thus increasing the strength ofthe connection portion.

In addition, the discharge path sections of the inner and outer bulbsare connected to each other through the connection portion to form asingle discharge path so as to increase the length of the dischargepath, thus enhancing the total luminous flux and the luminousefficiency.

Further, in the present invention, the distance between one of thepaired electrodes and the second electrode is smaller than the distancebetween the paired electrodes. When, prior to the occurrence ofdischarge between the pair of first electrodes of the illumination tubeto illuminate the fluorescent lamp, the discharge is caused to occurbetween the first electrode and the second electrode of the bulb, andthe discharge is then caused to occur between the pair of firstelectrodes of the illumination tube, the starting voltage for theillumination tube can be reduced. Alternatively, it is possible to causea primary discharge for illumination to occur only between the firstelectrode and the second electrode of the bulb, to provide a dimmerillumination of the fluorescent lamp.

In addition, according to the present invention, when the centers of theradii of curvature of the respective bent portions of the inner andouter bulbs, which are connected concentrically to each other, it ispossible to make the gap between the adjacent bent portionssubstantially equal to the gap between the straight tube portions, thusimproving the external appearance and providing a uniform brightness.

1. A fluorescent lamp comprising: a multi-ringed bulb including: aplurality of ring bulbs in which a plurality of straight tube portions,each having an outside diameter of from 12 to 20 mm, are connected toeach other through bent portions on a same plane, said ring bulbs beingplaced concentrically on the same plane; electrodes providedhermetically at respective ends of outermost and innermost bulbs of theplurality of ring bulbs; and a connection portion connecting otheradjacent ends of the outermost and innermost bulbs to each other so thatthe outermost and innermost bulbs communicate with each other to therebyform a single discharge path; a phosphor layer formed on inner surfacesof at least the straight tube portions of the multi-ringed bulb; and adischarge medium with which the multi-ringed bulb is filled, whereineach of the straight tube portions has a length “l ” of from 150 to 500mm, and a radius of curvature “r ” of the bent portion satisfies anexpression of 0.03 ≦r/l ≦0.3.
 2. The fluorescent lamp according to claim1, wherein each of the multi-ringed bulbs is formed by bending a singlestraight tube bulb member, said straight tube bulb member having a tubelength of from 800 to 2500 mm, a length of a bent-portion-formationprearrangement portion, which is to be formed into the bent portion,being within a range of from 5 to 50% of a total length of the straighttube bulb member.
 3. The fluorescent lamp according to claim 1, whereinsaid multi-ringed bulb comprises a double-tube bulb having inner andouter bulbs, electrode-side outer ends of the inner and outer bulbs atwhich a pair of electrodes are hermetically provided, respectively andother outer ends of the bulbs, which has the connection portion, arespaced apart from each other by a predetermined distance so as to faceeach other, and a base is disposed on one ends and other ends of thebulbs so as to cover respective end portions thereof.
 4. The fluorescentlamp according to claim 3, wherein the inner and outer bulbs connectedto each other through the connection portion are cut by fusion at theother outer end portions thereof and closed hermetically, and a minimumlength from the outer end portions to the connection portion is equal toor less than 15 mm.
 5. The fluorescent lamp according to claim 3,wherein each of the inner and outer bulbs is formed into a rectangularshape and both electrode-side ends of the inner and outer bulbs extendto corners of the rectangular shape.
 6. The fluorescent lamp accordingto claim 3, the bulbs are filled with mercury vapor serving as thedischarge medium, the connection portion is provided so that a least apart of the connection portion is substantially flush with the otherouter end portions of the inner and outer bulbs, and the electrode forthe outer bulb is positioned at a position apart from the end of thebulb by a distance, which is larger than a distance by which theelectrode for the inner bulb is positioned at a position apart from theend of the bulb.
 7. The fluorescent lamp according to claim 3, whereinthe electrode-side outer end of at least one of the inner and outerbulbs terminates at a position, which is disposed on an inner side in anaxial direction of the bulb relative to the electrode-side outer end ofthe other bulb, and electricity receiving devices are disposed on anouter surface of the base covering both the electrode-side outer endportions of the inner and outer bulbs corresponding to positions in aspace extending outward from the electrode-side outer end portion of theone of the inner and outer bulbs in the axial direction thereof.
 8. Thefluorescent lamp according to claim 3, further comprising a secondelectrode disposed at the end of the bulb corresponding to anintermediate position of the discharge path.
 9. The fluorescent lampaccording to claim 3, wherein centers of radii of curvature of inner andouter surfaces of bent portions of the inner and outer bulbssubstantially coincide with each other and the bent portions have adiameter, which is substantially identical to the diameter of thestraight tube portions disposed in a vicinity of the bent portions. 10.The fluorescent lamp according to claim 3, wherein each of the inner andouter bulbs is formed into a rectangular shape by four straight tubeportions, three bent portions are arranged at three diagonal positionsof the rectangular shape and the base is disposed at a remaining onediagonal position thereof.
 11. The fluorescent lamp according to claim3, wherein each of the inner and outer bulbs is formed into arectangular shape by five straight tube portions, bent portions arearranged at diagonal positions of the rectangular shape and the base isdisposed at a central position of one side of the rectangular shape. 12.A lighting apparatus comprising: a main body; a plurality of fluorescentlamps recited in claim 3; and a high frequency lighting circuit, whichsupplies lamp electricity to the fluorescent lamps at a high frequencyof at least 10 kHz.